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The declaration of Zika virus as a public health emergency will result in much-needed research being fast-tracked, Health Minister Jonathan Coleman says.

The World Health Organisation made the designation yesterday, an action it has taken only three times before, and which paves the way for the mobilisation of more money and manpower to fight the pathogen spreading "explosively" through the Americas.

Zika, first identified more than 50 years ago, has alarmed public health officials in recent months as it is potentially linked to thousands of cases of brain defects in newborns.

Estimates are the virus will infect up to four million people in the coming year.

In New Zealand, there have now been 10 Zika cases - eight confirmed - this year, affecting travellers arriving from Tonga, Samoa, and American Samoa.

Dr Coleman said the threat within New Zealand is virtually non-existent because of the lack of the mosquito species, Aedes aegypti, which is spreading the disease.

"New Zealanders are only at risk if travelling to areas where Zika is prevalent," Dr Coleman said.

"Until more is known about the virus, pregnant women or women planning to become pregnant should consider delaying travel to areas with Zika virus. Anyone travelling to Zika-infected countries should take appropriate precautions to avoid mosquito bites."

WHO director-general Margaret Chan said there was no reason for travel or trade restrictions at this time.

Much of the alarm comes from reports from Brazil, the epicentre of the outbreak, where Zika is suspected to have caused thousands of babies to be born with abnormally small heads and incomplete brain development. Researchers are also investigating a possible link between the virus and a surge in Guillain-Barre syndrome, a rare condition that can lead to paralysis.

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Air New Zealand has joined a growing number of airlines offering fare flexibility to pregnant travellers worried about travelling to Zika virus-affected areas.

Travel agents are also urging customers to take precautions, with one reporting a cancellation.

Air New Zealand said customers who were pregnant, and their travelling companions, could change their tickets if they met certain criteria.

If ticketed before January 22, passengers can change the date of travel without penalty or change their travel to another of the airline's destinations without penalty, although any difference in fares would apply.

Air New Zealand said it would would continue to monitor the situation.

Flight Centre said it had one cancellation due to the Zika virus, from a traveller to Samoa.

Travel insurance companies were assessing cases on an individual basis, he said.